Switching from Oil to Gas with big old radiators

I was so happy when NStar connected us to the new gas line on our street, am planning to switch from oil to gas for heat and HW, for fuel savings and more even heating performance.
Hoping to take advantage of any high efficiency rebates and zero interest loan.

Our house was built in 1900, colonial style, 3 floors ~2300 sq ft. Lots of original double hung sash windows with storms.
Very little insulation in the walls, not so great in the attic, and definitely some air infiltration.
Near Boston, Outdoor design temp i think is 9 degrees

Current oil fueled boiler is Utica SFH4150WT 175K showing 152,200 BTU/hr on plate.
Current hot water is 50 gallon electric heated.
Boiler is about 20 years old, we used 1350 gallon of oil in past 12 months.
We have 7 large cast iron radiators, 60 ft of cast iron baseboard, and 30 ft of newer fin baseboard.

I thought it would be a snap to move to a high efficiency gas boiler and set about getting 3 quotes before the dirt was settled over the gas line...
Quote 1 was for a Rinnai E110C combi unit to go with "on demand" HW.
They sent me a Manual J that said my heat load was 68,849 but it lists 2 "rooms" each at 1320 sq ft each? seems like a shortcut estimate

Quote 3
Spoke to an experienced plumber who has worked in a lot of houses.
He had concerns about the high efficiency mod-cons performing well with the large volume of water. He thinks they would not run at the high efficiency levels in a high mass system, and recommended:
Burnham ES2-5 which has a large cast iron boiler and can be vented out of current chimney (w addition of flue liner) and a Heat-Flo 50 gallon IHW storage.
Also recommends Outdoor Reset. He said we'd have to do a real manual J room by room measures so he could properly size the boiler, but he thinks the ES2 family would be a better fit for our radiators.
Problem is that burner is only 85% rated, so not only does not qualify for any rebates, but would not qualify for the 0% loan.

So let's assume that whomever does the proper sizing (I stopped by my library and have been reading Audel HVAC Fundamentals: Volume 1: Heating Systems, Furnaces and Boilers and started my own spreadsheet based on Chaps 3 and 4 !) - in the real world, can the new high efficiency mod con burners be installed and tuned to support high mass? I am pretty sure I want the Indirect HW.
Also, we are hoping to get better performance that we have now, where it takes awhile for the radiators to get warm, then they are really hot for while, then it cools down for an hour or two and then heats up again - thermostat just sits at 66 all days....

Hadn't thought all the details until we got into this process and then i started reading tons of stuff on line and then the Audel books...

We will try to mitigate insulation issues, but have siding on top of asbestos shingles so can't fill walls from the outside, a lot of issues like that...

Just trying to understand the pros and cons of any choices, thanx for any advice or ideas.

I've had nothing but problems with my Alpine 150 (I got it at a large discount when switching from oil to gas). From finding a qualified installer to install it correctly, to finding that the installer grossly oversized the unit, and now problems with reliability during Sandy when the control module was fried and I just spent more than 3 weeks without heat or hot water. Burnham from a customer service standpoint has been very unhelpful. I would not recommend becoming a customer of theirs.

If you can overcome those issues, my Alpine works great with cast iron high mass baseboard now that I got all the tweaking done.

My dad installed an ES-2 boiler last year with outdoor reset and has had zero problems with it.

I've had nothing but problems with my Alpine 150 (I got it at a large discount when switching from oil to gas). From finding a qualified installer to install it correctly, to finding that the installer grossly oversized the unit, and now problems with reliability during Sandy when the control module was fried and I just spent more than 3 weeks without heat or hot water. Burnham from a customer service standpoint has been very unhelpful. I would not recommend becoming a customer of theirs.

If you can overcome those issues, my Alpine works great with cast iron high mass baseboard now that I got all the tweaking done.

My dad installed an ES-2 boiler last year with outdoor reset and has had zero problems with it.

Last year was on the mild side for Boston, so if you're inside 128 near the water it was about a 4500 heating degree day season, but outside of 128 it was at least 5000- 5500 HDD. Let's assume 5000HDD.

162,081,000 BTU used over 5000 HDD is 158,355,000/5000= 32,416 BTU per degree-day.

With 24 hours in a day that's 32,416 BTU/24hr= 1350 BTU per degree-hour.

Using 99% outside design temp of +10F to make the math easy, (Boston's design temp is +12F), and a presumed balance point of 65F (the base temp for the HDD, it'll be close), you get:

65F - 10F = 55 heating degrees.

So at 1350 BTU per degree hour the heat load at design temp is about 1350 x 55= 74,250 BTU/hr.

Since the boiler is about 2x oversized, it means that your actual AFUE was at best ~5% lower than the 87% nameplate rating, meaning it's actually about 70KBTU/hr.

Quote #1's heat load calc wasn't insane, but they probably did it floor-by-floor rather than room-by-room to save time. While Rinnai sells more gas-burners than any other appliance worldwide, the domestic hot water aspects of combis kinda suck. A boiler sized for the space heating load and an indirect sized for the largest tub in the house is usually more satisfactory on all fronts.

Quote #2 sizing is just nuts, and would be a LOUSY way to set up the system! (What, you need to be good down to -60F? That might make sense in Fairbanks AK, but Beantown hasn't seen that temp since the last ice age!) The indirect is fine, but by the time you insulate & air seal you'll be good down to colder than -100F outdoor temps with boilers that size which is triple-crazy.

Quote #3 is similarly nuts. If mod cons can work great with massive radiant floor slabs (which they very much DO), designing them into high-mass radiators is similarly nice. Where they (and other boilers) run into problem is with LOW mass radiation (like fin-tube), where it's all been micro-zoned to the -nth degree.

What makes sense is a right-sized boiler for the "after" picture of any planned weatherization upgrades, an that will be almost certainly under 50KBTU/hr output, possibly under 40K.

You have a lot of low-hanging fruit on load reduction- start with air-sealing, but then move onto all of the easy insulation. MA has a lot of very good subsidies for weatherization, and spending a couple grand (after subsidy) on air sealing & insulation should bring a house that vintage & size under 50K, probably under 40K while increasing your comfort level considerably. (For reference, I live in a ~2400 ca 1923 1.5 story bungalow in Worcester. When I moved in the heat load was about 50K @ +5F, but after some judicious tightening & insulation it's now well-under 40K. That's with the original double hung windows w/clear-glass storms, ~R20 in the cathedral ceilings that comprise most of the top-side-insulation, and known gaps in the wall insulation. If you want to take it down to 35K & lower you'll have to insulate the foundation, but getting under 50K should be fairly no-brainer easy, and relatively cheap. The key place to start on a 3-story is to air-seal both the attic floor and at the foundation sill/band joist to kill the stack effect driven infiltration. This includes any balloon-framing (== flue) and around flue & plumbing chases, electrical penetrations in the upper floor ceiling, and any dryer/other venting in the basement. The foundation sill is usually a bigger air leak than all of the windows & doors combined, and 2" of closed cell foam at $2-2.50/square foot to insulate and seal the band joist is almost always going to reduce the heat load far more than the mere R-value of the foam would indicate. The taller the house, the more important that is.

If balloon-framed (many ca 1900 houses are) you may be able to dense-pack cellulose into the walls primarily from the attic,&/or basement with a few well placed holes to deal with window-framing blockages. (I did most of my wall insulation blowing from the basement, despite plated framing rather than balloon framing.)

Back to boiler picks: The Triangle Tube Solo-60 is very popular, and has good regional support, and would probably handle the current heat load on all but the coldest nights.

The Peerless Pinnacle T-50 would handle the "after" weatheriztion picture, and the T-80 would handle the "before" picture.

There are many good boilers out there in that size range, but find somebody who actual "gets-it" on how to design for condensing efficiency. With high mass (and oversized for the heat load post-insulation) radiator a mod-con can be tweaked to run 100% of the time in condensing mode. It's also worth digging up 30' of craigslist cast iron baseboard to replace your fin-tube (or if you're feeling flush, buy some new stuff at $40-50/foot) since fin-tube will crap out with very non-linear output at very low condensing water temps where cast iron is predictable comfortable and nice, even with 85-90F water, which is probably where you'd be able to run during the shoulder seasons under outdoor reset control.

BTW: If you have a mid or late-winter oil bill with a "K-factor" stamped on it, that single number puts a stake in the ground for boiler sizing. K-factor to an oil-guy is degree-days per gallon of oil (rather than BTU/HDD), so you can work from there to get to the same arithmetic I used in the above example where I'd merely guesstimated the HDD.

I'm in Needham so right on the Rt 128 line, definitely warmer than Worcester!
I just had MassSave in here this week (it's required to be eligible for the zero interest loan) and most of the helpful insulation stuff will be a project - I have a 3rd floor that has 2 rooms that have some kinda dropped ceiling that may have been a DIY project way back when, so MassSave couldn't do any Sealing or insulation work above in the attic unless I replaced that to real weight bearing code. Room # 3 on the 3rd floor is a true uninsulated attic but all 3 spavces have floorboards, so to get to ceiling of the 2nd floor rooms, you'd have to pull up floorboards (some but not all?) on the 3rd floor. As for trying to get insulation into the walls, it was near impossible to get a coaxial cable into a 2nd floor room from the basement following an electrical line (may be more a reflection on my skills tho). I'd love to get good advice and cost estimates from someone who does this to get an idea of what would be involved but it seems non trivial. Basement stuff should be doable, it is drafty down there...

Sounds like I just need to find an installer who will do a real heat loss, although if Quote #1 is close using the "sq ft per floor as a room" approach and came up w 69K, then even if the real load is ~ 50K, could he go with a Rinnai Q85S with a range of 17,000- 85,000 BTU for boiler and a 50 gallon IHW, and then it's just a matter of tuning (with Outdoor reset) ? AS long as the lower and upper ranges of a mod-com cover my heat load range, that would work, right? Not sure how to get more info on pros & cons of different manufacturers that are in the same ballpark, like the Burnham Alpine 105 (21-105,000). I want solid quality (not the cheapest) and I also need local support and service, and of course would love to get as much rebate on any unit if it's the right one...

btw, Quote 1 was a contractor listed in the NStar gas conversion packet, they installed for a neighbor who was happy.
Quote # 2 was my current Oil company (trying to make up for my lost oil revenue on my way out?)
Quote # 3 is a local plumber.

The Alpine 80 is the biggest I'd go on that line- the -105 is still too much boiler.

The early season K-factors have to be thrown out since they don't reflect continuous heat loading. The mid- to late-winter average seems to be ~4.2 HDD/gallon, or 4.2 HDD/138,000 input BTUs. Inverting that to BTU/HDD you get 32,857 input-BTU/HDD, which in an 87% burner is 0.87 x 32857= 28,585 BTU/HDD heating the house.

/24 hours per day is 1191BTU/degree-hour. So at 56 heating degrees (65F balance point, minus the desing temp of +9) gives you 66,700BTU/hr for a design condition heat load, not more. If you sized it EXACTLY with a 66.7K output, you'd never wake up to a cold house in a normal year, but you might fall a few degrees short during the coldest night over 25 a year period.

[edited for grammer & clarity, and to add]

Running the Burnham Alpine 80 even at above-condensing temps it still has over 70 KBTU/hr of output- it's more than enough boiler, even for the "before" picture.

Morgan, it sounds like the Contractor #1 (the Rinnai guy) did a reasonable quick & dirty heat load- probably with a piece of crummy software, since it aligns pretty well with fuel-use data (not that the proposed solution was such a clear winner.) Room by room heat loads would be useful if there were adjustments being made to the radiation as part of the system upgrade, but since it isn't, the whole house load is good enough for sizing a boiler.

But clearly the other proposals are off-the charts silly options. Almost any of the smallest-of-line mod cons would heat this house with (and often without) the weatherization upgrades. A contractor who understands mod-cons who will at least do an quick I=B=R spreadsheet heat load estimate using best-guesses on the construction & U-factors would get you there. It doesn't have to be a commercial heat load tool (even a cheapie/freebie), or even room-by-room analysis for a decent pro to get to a reasonable solution.

Contractor # 2 is just plain lazy & /or ignorant by only proposing units with output comparable to the existing oversized unit.

Contractor # 3 is probably just ignorant about how to set up mod-cons, but he was at least recommending doing a Manual-J first. But getting a mod-con to maintain a constant room temp with nearly full-time condensing mode by dialing in the ODR curve isn't rocket science, and there's zero advantage to going with an oversized high-mass boiler + ODR as he was recommending- find a different contractor.

Look up the local distributors are for some of the likely-candidate mod-cons and ask the distributor to recommend a few contractors. They are in a good position to know who is installing them by the dozen with few call-backs, and who are the illiterates constantly on the line with tech support to figure out what is clearly spelled out in the manual.

Dana. Your analysis is correct and conclusions crystal-clear as usual.

In Minneapolis/St.Paul and surrounding suburbs you must have a steam and hot water license and a heat load analysis must be sent to the city before a permit is issued before an old boiler is replaced with a new one. This is rare in the US, as most heating contractors have no license at all. Fact is, when taking the various tests for boiler, plumber and pipe fitter in the Twin Cities, not one question about heat loads appeared.

The contractor is key. Every manufacturer of boilers provides some sort of training on the subject but relatively few take advantage. Mostly because they install few boilers. Unfortunately the majority of boiler installers seem to be stuck in the 50's and will not install condensing boilers.

Calling the local distributor is easy enough. They will recommend people who pay their bills, buy a lot of boilers from them or at least someone to whom they are related.

Fact is, the boiler distributors - or the salesman that work for them - do the bulk of residential heat loads for the contractors (better than nothing). The remainder are performed by the contractor or more often, WAGed.

I tell my clients to choose from the few contractors that can produce a sample heat load and avoid the low bidder.

It is a sad state of affairs, 25 years after I installed my first ModCon.

I bought my house in Oct 2012 and it still had the original 1940 oil boiler, so I don't know the efficiency or fuel cost of the oil system. However, I already had a gas line for the water heater and stove, so I started getting estimates on a replacement gas boiler. I finally settled on a Buderus GC124 with electronic ignition as a basic replacement that would fit my budget better than the more expensive units. It went in very smoothly as a replacement system and I've been very happy with the combination of the Buderus and a Honeywell setback thermostat. Gas bills are reasonable, and the system does a good job of keeping heat even in this older home.

We install the GC124 Buderus cast iron boiler but recommend outdoor reset over setback thermostats (designed for forced air discomfort). You have a good boiler and it should last about 30 years at 84% AFUE. Sizing low-efficiency cast iron boilers is not quite as critical as sizing condensing boilers as expectations are lower and control strategies will never overcome that 350Â°F stack temperature.